1. Field of the Invention
This invention relates to apparatus and method for coding of graphic information to facilitate editing, storing and transmitting such information in a compact and efficient manner.
2. Description of the Prior Art
Creation of new engineering drawings on cathode-ray tube (CRT) graphics terminals with the help of computer-aided design and drafting (CADD) techniques not only results in an intelligent, compact data file, but also facilitates the rapid retrieval and updating thereof to incorporate future changes. The benefits of CADD can be realized most directly in applications such as building space planning and layout, as well as electronic, automotive and aircraft structural design. However, the current practice of entering existing drawings into computer graphics systems by manual methods is costly and time-consuming.
A number of techniques have been proposed in recent years for coding facsimile transmissions to reduce bandwidth occupancy. Most such techniques rely on one-dimensional encoding of raster scan lines through observations of the coordinates of transitions between black and white light values in graphics material. For storage and transmission purposes black lengths of scan line can be encoded by the locations of the white-to-black transitions and the distances to succeeding black-to-white transitions. Such one-dimensional coding is known as run-length coding. As early as 1952 D. A. Huffman in his paper entitled "A Method for the Construction of Minimum Redundancy Codes" (Proc. IRE, September 1952, pp. 1098-1101) described the construction of a minimum redundancy code based on run length statistics to reduce the average number of coding bits per image.
More recently A. J. Frank has described two-dimensional coding extending over contiguous scan lines by means of which "blobs" of graphics material can be defined as a single entity in U.S. Pat. No. 4,107,648 granted Aug. 15, 1978. In the introductory section of her specification Frank describes the background of two-dimensional encoding of graphics material in considerable detail. Such description is herewith incorporated by reference into the present specification.
It is an object of this invention to encode line lengths in engineering drawings digitally by the coordinates of their start and finish picture elements and line thickness.
It is another object of this invention to provide a vector coding technique for compacting the digital storage requirements of engineering line drawings in particular and graphic images in general.
It is a further object of this invention to provide an efficient vector coding technique which extracts vector information in real time from raster-type data scanned line by line.
A specific advantage of digitization of engineering drawings is the capability of editing and amending from remote terminals.